There has been a well recognized need for fast, reliable and inexpensive analytical techniques for detecting the presence of chemical and/or biological analytes, and/or quantifying the amount of chemical and/or biological analytes present in a sample. Conventional analytical chemistry techniques, such as chromatographic techniques, mass spectrometry, titration, etc. can provide reliable results. However, these conventional analytical techniques are generally time consuming and expensive. Further, they are generally performed in a laboratory at a fixed location, and are not easily portable or adaptable for portable use.
Chemical and/or biological sensors have been developed to overcome some of the disadvantages with conventional analyte detection techniques. The known chemical and/or biological sensors are generally composed of two distinct functional components: a sensing element and a transducer. The sensing element chemically interacts with the analyte of interest to induce changes in some detectable physicochemical property, and the transducer detects these physicochemical property changes and converts them into a measurable output signal.
Most chemical and/or biological sensors can be categorized as optical, resistive, electrochemical or acoustic mass sensing devices. Often complex instruments, such as high-resolution charge-coupled devices (CCDs) with optical fiber sensors or electronic oscillating circuitry with surface acoustic wave (SAW) mass sensors, are required to operate known chemical and/or biochemical sensors. Preferred for chemical and/or biological sensors are optical devices that rely on calorimetric, fluorimetric or fluorescence depolarization sensors, wherein the molecular recognition event triggers a drastic color change that is observable by the naked eye and/or is quantifiable by optical absorption using spectroscopic instrumentation. A particularly promising step in this direction is a recently disclosed system of conjugated polymer vesicles that are bonded together with a polydiacetylene (PDA) backbone. When conjugated to biologically interactive carbohydrates such as sialic acid and ganglioside GM1, the resulting highly colored polymerized v change in the presence of influenza virus and cholera toxin, respectively. Such color changes result from perturbation of PDA structural conformation and the extent of uninterrupted conjugation, which is typically caused by heat, organic solvents, changes in pH, or mechanical stress.
Among the various classes of well known polymerizable organic functional groups, diacetylenes are rather unusual in that a highly ordered state is required for their polymerization to occur. In practice, polymerization has been achieved when diacetylene monomers are locked in solid state conformations such as crystal lattices, Langmuir-Blodgett (LB) films, self-assembled monolayers (SAM) or vesicles, thereby allowing polymerization to proceed by repeated 1,4-addition of the diacetylene monomers. This type of geometrically constrained polymerization reaction (illustrated in FIG. 1) is referred to as a “topochemical polymerization,” and it is typically initiated by heat or irradiation from an ultraviolet or gamma radiation source. The resulting polymers have highly conjugated segments, composed of alternating conjugated double and triple bonds along the backbone, and as a consequence of this conjugation they are usually highly colored. For example, in the case of polymerized vesicles the predominant colors are blue, red or violet.
However, the reported PDA vesicle system has significant limitations. First, since vesicle formation is based on self-assembly at the molecular level, it does not offer direct control of molecular architecture, resulting in a variety of different sizes and shapes when lipids randomly self-assemble into vesicles. Secondly, although polymerized lipids are dispersible in aqueous media, they are not truly soluble, and therefore lack the kinetic and thermodynamic advantages that a truly homogenous assay would offer.